The present invention relates to radio transceivers and more particularly to a radio-frequency output level compensating circuit for use in full duplex portable radio transceivers powered by a battery.
The cellular type mobile communication device was originally intended for use as a vehicular radio-telephone, but, currently, development has been directed towards a portable radio-telephone. Accordingly, development in the operational method of a cellular system also tends to change from being focussed on the conventional vehicular radio-telephones (with a transmitting output level in Class 1 and having a maximum transmitting output power of three Watts) to focussing on portable radio-telephones (with a transmitting output level in Class 3 and a maximum transmitting output power of 0.6 Watts). That is, with an increase in cells (microcells), users are able to communicate by using the transmitting output power of portable radio-telephones. In spite of this state of development however, there remains a problem because it is difficult for a user attempting to use portable radio-telephones to make a radio-call due to the location from which the portable radio-telephone is used. Portable radio-telephones are frequently used in vehicles because of their special characteristics. When a portable radio-telephone is used in a vehicle however, a radio wave is attenuated by the body of the vehicle, so that an actual radio-frequency signal transmitted or received through an antenna of the portable radio-telephone is attenuated. Accordingly, the user has difficulty in making a radiotelephone call.
A conventional circuit to solve the aforementioned problem has been disclosed in U.S. Pat. No. 4,636,741, issued 13 Jan. 1987 to James E. Mitzlaff. A vehicular adaptor is installed in a vehicle, and a multi-level power amplifier is mounted in the portable radio-telephone, so that the radio transmitting signal level is boosted when the portable radio-telephone is connected to the vehicular adaptor.
In Mitzlaff's circuit, if the portable radio-telephone is connected to the vehicular adaptor installed in a vehicle, a vehicular antenna is connected by means of a connector instead of the portable radio-telephone's antenna, and a voltage supplied to the multilevel power amplifier composed of multiple stages is supplied by the vehicle battery instead of the portable radio-telephone's battery. Also, the output level of the power amplifier in the portable radio-telephone is switched to a higher output level of Class 1 with a maximum output power level of three Watts rather than to an output level of the Class 3, 0.6 Watts maximum output power level of the portable radio-telephone, so that the power amplifier can transmit at a higher output level.
As described above, the typical conventional circuit operates with a transmitting level of "Class 3" when the multi-level power amplifier for the portable radio-telephone uses the battery of the portable radio-telephone. When a power source of a vehicle battery, which is larger than that of the battery of the portable radio-telephone, is connected and then used, the power amplifier is operated with a transmitting level of "Class 1", thereby solving the problem created when the portable telephones are used in vehicles.
However, when the multi-level power amplifier positioned within the portable radio-telephone for providing power amplification of the radio-frequency is operated at a level of "Class 1", its transmitting output level is high. The circuit of the portable radio-telephone should therefore use components which are capable of providing such an output. Accordingly, as the size of components of the multi-level power amplifier become larger, a heat emission processing device is also needed. This brings a problem of enlarging the size of portable radio-telephones. Particularly, when the portable radio-telephone is used for a long period of time, the heat generated during high output transmission is spread over the body of the portable radio-telephone. This causes a problem of providing an unpleasant feeling to the user, such as the portable radio-telephone being too hot to handle.
Also, the maximum three Watt transmitting output level of the power amplifier at the final stage, among the multi-level power amplifiers that are connected in cascade form using at least two or more power amplifiers, is higher than the maximum output of 0.6 Watts of the pre-power amplifier which inputs and power-amplifies the radio frequency signal. Thus, the magnitude of the power source supplied to the final output power amplifier should be higher than that of the power source supplied to the pre-power amplifier. To implement this, another extra power source would need to be supplied, and, as a result, the power source circuit becomes complicated.
The Vehicular Power Booster Circuitry For Multi-Level Portable Transceiver described in U.S. Pat. No. 5,193,219 to Yoshihara Tamura corrects for the enlargement of the Mitzlaff transceiver and its extra weight by contemplating the use of a booster having several operating voltage levels for use when the portable transceiver is mounted in a vehicle. The voltage level used in boosting the transmitting power is selected in response to a difference in an output level of the portable transceiver and an output level of the amplifier of the booster to keep this difference to a minimum.
The Method and Apparatus for Reducing Power Consumption In A Radio Telecommunication Apparatus disclosed in U.S. Pat. No. 5,203,020 to Sato et al. automatically disconnects the antenna and battery of the portable transceiver and connects the vehicle's battery and antenna to the portable radio telephone when mounting the portable radio telephone to the vehicle in response to the detection of the higher voltage supplied by the vehicles battery.
The Radio Communication Device and Method of Controlling Transmitter Output Level for a portable transceiver mountable in a vehicle disclosed in U.S. Pat. No. 4,654,882 to Shigeki Ikeda contemplates the controlling of the output transmitting power of the portable unit to a minimum level required for input to the amplifier of the fixed (vehicle mounted) unit to compensate for excessive heat. The Ikeda device uses the vehicle's battery and antenna when the portable unit is connected thereto.
The Portable Telephone With Power Source/Mode Change During Calls by Metroka et al. in U.S. Pat. 5,036,532 teaches the use of a vehicle's battery (see, e.g., FIG. 6) to operate the portable radio telephone by connecting the portable radio telephone to a mobile transceiver adaptor mounted in the vehicle. This arrangement however, relies upon a mobile transceiver and its antenna to improve transmission power and reception sensitivity, instead of the portable radio telephone's cellular transceiver and antenna.